The present invention is related generally to fluid control systems and, more particularly, to a uniquely configured valve controller assembly having a deterministic digital controller with increased input and output capabilities and being configured to operate under a reduced cycle time and which is packageable in a small, explosion-proof and waterproof container that can optionally be located near the valve(s) to be controlled.
Steam turbine power plants typically employ steam as a working fluid wherein a turbine section of the power plant extracts heat from the steam for conversion to mechanical energy and, ultimately, for the generation of electricity. A turbine bypass system is typically included in many steam turbine power plants. The turbine bypass system may include a turbine bypass valve as a means to divert steam continuously produced by the boiler around the turbine section. The turbine section itself may be comprised of several turbines which may be arranged in series. A reheater may be included between each one of the turbines for reheating the steam after passing through each turbine. After exiting the turbine section, the steam may be delivered to a condenser wherein the steam is transformed into water which may be recycled to the boiler.
When the turbine bypass system is actuated, the heat of the steam which would otherwise be extracted by the turbines must be cooled in order to prevent damage to the reheater and the condenser as a result of thermal shock. One method of reducing the temperature of the steam in the bypass system is to inject a spray of cooling water into the flow of superheated steam. The amount of cooling water that is sprayed into the flow of steam must be controlled in order to prevent other problems to downstream components. For example, if an excess amount of cooling water spray is injected into the flow of the superheated steam, complete mixing and evaporation of the cooling water spray will not occur and the non-evaporated cooling water may cause damage to system components.
Various controller configurations have been developed in the prior art in order to control both the turbine bypass valve as well as the spray water valve. Typically, controllers receive various sensor inputs such as steam temperature, steam flow rate, cooling water spray flow rate and other parameters such as the position of the turbine bypass valve and the spray water valve in regulating the turbine bypass system. Such parameters must be accurately measured and processed by the controller in order to allow for accurate control of the turbine bypass valve and spray water valve.
The accuracy with which the controller regulates such valves can impact the operating efficiency of the power plant and can have a bearing on the life expectancy and maintenance requirements. As may be expected, an increased quantity of input signals in the form of field measurements of temperature, flow rate, and valve position can result in a proportionate increase in controller accuracy, stability and reliability.
Many of the prior art controllers which have been developed are limited in the amount of data inputs that can be processed. In addition, many prior art controller are limited to installation in control rooms necessitating the routing of multiple communication lines (i.e., cabling) from the controller to the valves of the turbine bypass system. Furthermore, many controllers of the prior art have a limited temperature range within which the controller can be reliably operated. Even further, many controllers of the prior art are unsuitable for installation in hazardous areas such as those commonly found in severe service environments in the oil and gas industry.
Perhaps an even more noteworthy deficiency of prior art controllers is the relatively lengthy scan time required in acquiring and processing the various input (i.e., sensor) signals and generating output signals that are necessary to regulate operation of the turbine bypass system. As may be appreciated, a lengthy scan time for the controller can result in reduced reliability, flexibility and efficiency in monitoring and regulating the operation of the turbine bypass system.
As can be seen, there exists a need in the art for a controller assembly capable of controlling a group of valves such as for a turbine bypass system and which is capable of quickly and accurately processing a large quantity of input signals and generating appropriate output signals. Furthermore, there exists a need in the art for a controller assembly which is capable of reliably operating in severe service applications within a wide range of temperature and humidity extremes. For example, there exists a need in the art for a controller assembly which is suitable for installation in hazardous areas that are commonly found in critical control environments associated with the power, oil and gas industries. Finally, there exists a need in the art for a controller assembly that provides the above-described features in a compact size to allow mounting in the field directly adjacent the valves to be controlled.